Emergence of Anchored Flux Tubes Through the Convection Zone

  1. J. H. Waite Jr.,
  2. J. L. Burch and
  3. R. L. Moore
  1. George H. Fisher2,
  2. Dean-Yi Chou3 and
  3. Alexander N. McClymont1

Published Online: 18 MAR 2013

DOI: 10.1029/GM054p0047

Solar System Plasma Physics

Solar System Plasma Physics

How to Cite

Fisher, G. H., Chou, D.-Y. and McClymont, A. N. (1989) Emergence of Anchored Flux Tubes Through the Convection Zone, in Solar System Plasma Physics (eds J. H. Waite, J. L. Burch and R. L. Moore), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM054p0047

Author Information

  1. 1

    Institute for Astronomy, University of Hawaii, Honolulu, HI 96822 and Institute of Geophysics and Planetary Physics, LLNL, Livermore, CA 94550

  2. 2

    Physics Department, Tsing Hua University, Hsinchu 30043, Taiwan, R.O.C.

  3. 3

    Institute for Astronomy, University of Hawaii, Honolulu, HI 96822

Publication History

  1. Published Online: 18 MAR 2013
  2. Published Print: 1 JAN 1989

ISBN Information

Print ISBN: 9780875900742

Online ISBN: 9781118664315



  • Space plasmas;
  • Sun;
  • Magnetosphere;
  • Astrophysics


We model the evolution of buoyant magnetic flux tubes in the Sun's convection zone. A flux tube is assumed to lie initially near the top of the stably stratified radiative core below the convection zone, but a segment of it is perturbed into the convection zone by gradual heating and convective overshoot motions. The ends (“footpoints”) of the segment remain anchored at the base of the convection zone, and if the segment is sufficiently long, it may be buoyantly unstable, rising through the convection zone in a short time. The length of the flux tube determines the ratio of buoyancy to magnetic tension: short loops of flux are arrested before reaching the top of the convection zone, while longer loops emerge to erupt through the photosphere. Using Spruit's convection zone model, we compute the minimum footpoint separation Lc required for erupting flux tubes. We explore the dependence of Lc on the initial thermal state of the perturbed flux tube segment and on its initial magnetic field strength. Following an investigation of thermal diffusion times and the dynamic rise times of unstable flux tube segments, we conclude that the most likely origin for magnetic flux which erupts to the surface is from short length scale perturbations (L<Lc ) which are initially stable, but which are subsequently destabilized either by diffusion of heat into the tube or by stretching of the anchor points until L just exceeds Lc . In either case, the separation of the anchor points of the emergent flux tube should lie between the critical distance for a flux tube in mechanical equilibrium and one in thermal equilibrium. Finally, after comparing the dispersion of dynamic rise times with the much shorter observed active region formation time scales, we conclude that active regions form from the emergence of a single flux tube segment.